1. Field of Invention
This invention relates to typewriters, particularly to a typewriter having an electronic data processing and communication system between the keyboard and the printing mechanism. More particularly, it relates to such a typewriter with error correction and halfspace offset registration features.
2. Description of Prior Art
Heretofore most typewriters contained a keyboard and a mechanical typing mechanism (typebars, ball, or printing wheel) which operated in response to actuation of finger keys on the keyboard. Complex mechanical linkages were provided for coupling motion from the finger keys to the typing mechanism in order to cause the characters selected at the keyboard to be typed. These linkages were awkward and were fraught with other disadvantages.
Recently, so-called "electronic typewriters" have appeared; in these the output of the keyboard consists of electronic signals which are processed in an electronic data processing system within the typewriter to generate suitable control signals for driving solenoids and step- or servo-motors to cause the typing mechanism to print the selected characters. One advantage of electronic typewriters over their mechanical counterparts is the elimination of the complex mechanical linkages between the keyboard and the typing mechanism. Another important advantage is the electronic typewriter's ability to "remember" the last plurality of characters typed so that if an error has been made, the typist can backspace to the location of the error, and automatically have the erroneous character recalled from the electronic memory and retyped over a correction ribbon so as to erase the erroneous character (or several erroneous characters) easily and rapidly, whereafter the correct character(s) can be retyped in the space freed by removal of the erroneous character. One such automatic erasing electronic typewriter is shown in U.S. Pat. No. 3,870,846 to Kolpek and Rahenkamp, granted Dec. 23, 1973.
While such error-correcting electronic typewriters have been able to work satisfactorily, their capabilities were limited because generally they could erase previously-typed erroneous characters and replace them with new, correct characters on a one-for-one basis only. However typing errors cannot always be corrected by a one-for-one erasure and replacement method inasmuch as it is often necessary to replace an erroneous character with several characters, or to replace an erroneous word with a word having more characters than the erroneously-typed word.
For example, assume that a typist types a word without one of its letters, such as the word "patnt", instead of "patent". Also assume that before detecting this error, the typist types one or more additional words. It was not possible, in prior art correcting typewriters, to insert the missing character ("e") in the erroneously-typed word since there was no space or other way to insert the missing character.
Similarly if a typist types a wrong word in a phrase, such as "he is here" when it was desired to have typed "he was here", mere erasure of the erroneous word "is" would not enable an appropriate correction to be made since there is not enough space left to type the correct three-letter word ("was") with leading and trailing spaces in the area occupied by the erroneous two-letter word ("is").
Accordingly, several objects of the present invention are to provide a new and improved electronic typewriter, to provide an electronic typewriter with improved and more versatile correction means, and to provide an electronic typewriter in which corrections can be made which are not restricted to replacement of erroneously-typed characters on a one-for-one basis. Further objects and advantages of the invention will become apparent from a consideration of the ensuing description thereof.